The issue of SF

6

is more and more concerned due to its greenhouse effect.C

5

F

10

O（C5）

C

4

F

7

N（C4）andtheir gas mixture with Air or CO

2

are considered as presently the most potential mediums to replace SF

6

.In this pa-per

based on the detachable experiment device and

the platform

lightning impulse characteristic of SF

6

and its al-ternative gases in uniform fields is studied experimentally with such two types of electrode structures as plate toplate and coaxial type.It is shown by the result that 50%breakdown voltage of SF

6

C5/air and C4/CO

2

increaseswith the rise of gas filling pressure.The rising rate of SF

6

is the maximum and that of C4/CO

2

is minimum.In case ofthe coaxial type structure

the influence of the polarity applied lightning impulse voltage on the breakdown voltageof both SF

6

and C4/CO

2

gas is relatively larger

but on that C5/Air is relatively small.In case of the plate to platestructure

50% breakdown voltage of the three kinds of gases shows near linear increase trend with the electrodeclearance.The higher the gas filling pressure is

the higher the linearity is.It is found from the dielectric character-istic ratios of the alternative gases to SF

6

that in the equipment with higher gas filling pressure

the application feasi-bility is greatly limited only by increasing the gas filling pressure of C5/Air and C4/CO

2

to improve its dielectric per-formance

while in case of application in the equipment with lower gas filling pressure

C4/CO

2

mixed gas has morefeasibility to replace SF

6

.